Blood collection and processing play important roles in the worldwide health care system. In conventional large scale blood collection, blood is removed from a donor or patient, separated into its various blood components via centrifugation, filtration, or elutriation and stored in sterile containers for future infusion into a patient for therapeutic use. The separated blood components typically include fractions comprising red blood cells, white blood cells, platelets, and plasma. Separation of blood into its components can be performed continuously during collection or can be performed subsequent to collection in batches, particularly with respect to the processing of whole blood samples. Separation of blood into its various components under highly sterile conditions is critical to many therapeutic applications.
Recently, apheresis blood collection techniques have been adopted in many large scale blood collection centers wherein a selected component of blood is collected and the balance of the blood is returned to the donor during collection. In apheresis, blood is removed from a donor and immediately separated into its components by on-line blood processing methods. Typically, on-line blood processing is provided by density centrifugation, filtration, or diffusion-based separation techniques. One or more of the separated blood components are collected and stored in sterile containers, while the remaining blood components are directly re-circulated to the donor. An advantage of this method is that it allows more frequent donation from an individual donor because only a selected blood component is collected and purified. For example, a donor undergoing plateletpheresis, whereby platelets are collected and the non-platelet blood components are returned to the donor, may donate blood as often as once every fourteen days.
Apheresis blood processing also plays an important role in a large number of therapeutic procedures. In these methods, blood is withdrawn from a patient undergoing therapy, separated, and a selected fraction is collected while the remainder is returned to the patient. For example, a patient may undergo leukapheresis prior to radiation therapy, whereby the white blood cell component of his blood is separated, collected and stored to avoid exposure to radiation.
Both conventional blood collection and apheresis systems typically employ differential centrifugation methods for separating blood into its various blood components. In differential centrifugation, blood is circulated through a sterile blood processing vessel which is rotated at high rotational speeds about a central rotation axis. Rotation of the blood processing vessel creates a centrifugal force directed along rotating axes of separation oriented perpendicular to the central rotation axis of the centrifuge. The centrifugal force generated upon rotation separates particles suspended in the blood sample into discrete fractions having different densities. Specifically, a blood sample separates into discrete phases corresponding to a higher density fraction comprising red blood cells and a lower density fraction comprising plasma. In addition, an intermediate density fraction comprising platelets and leukocytes forms an interface layer between the red blood cells and the plasma. Descriptions of blood centrifugation devices are provided in U.S. Pat. No. 5,653,887 and U.S. Pat. No. 7,033,512.
To achieve continuous, high throughput blood separation, extraction or collect ports are provided in most blood processing vessels. Extraction ports are capable of withdrawing material from the separation chamber at adjustable flow rates and, typically, are disposed at selected positions along the separation axis corresponding to discrete blood components. To ensure the extracted fluid exiting a selected extraction port is substantially limited to a single phase, however, the phase boundaries between the separated blood components must be positioned along the separation axis such that an extraction port contacts a single phase. For example, if the fraction containing white blood cells resides too close to the extraction port corresponding to platelet enriched plasma, white blood cells may enter the platelet enriched plasma stream exiting the blood processing vessel, thereby degrading the extent of separation achieved during blood processing. Although conventional blood processing via density centrifugation is capable of efficient separation of individual blood components, the purities of individual components obtained using this method is often not optimal for use in many therapeutic applications.
As a result of the inability to achieve optimal purity levels using centrifugation separation alone, a number of complementary separation techniques based on filtration, elutriation in a cell separation chamber and affinity-based techniques have been developed to achieve the optimal purities needed for use of blood components as therapeutic agents. These techniques, however, often reduce the overall yield realized and may reduce the therapeutic efficacy of the blood components collected. Exemplary methods and devices of blood processing via filtration, elutriation and affinity based methods are described in U.S. Pat. No. 6,334,842.
A centrifugal blood component separation apparatus has been described in commonly assigned U.S. Pat. No. 7,605,388, for instance. As described in U.S. Pat. No. 7,605,388, an optical cell may be configured such that white blood cells can be extracted through a first extraction port, plasma and/or platelets can be extracted through second extraction port, and red blood cells can be extracted through third extraction port. As also mentioned in U.S. Pat. No. 7,605,388 (but not shown), optical cells of a blood separation vessel can include one or more dams positioned proximate to the extraction ports to facilitate selective extraction of separated blood components having reduced impurities arising from adjacent components. The use of dams in blood processing via density centrifugation is known in the art and described in U.S. Pat. Nos. 6,053,856; 6,334,842 and 6,514,189.